Chronic idiopathic urticaria is the medical term for hives, and doctors usually refer to it as chronic spontaneous urticaria. Although there are no known causes, various triggers may include allergies, pets, medications, and foods.

Urticaria means hives, or an itchy rash of welts on the skin. Idiopathic means that doctors do not know the underlying cause of the condition, which occurs spontaneously.

Idiopathic urticaria is a chronic, or long-term, condition when the symptoms come and go for at least 6 weeks. Doctors think that the condition is an immune system response, despite not knowing the exact mechanism behind why it happens. However, they do know a number of triggers that can bring on the hives.

This article explains what can trigger chronic idiopathic urticaria.

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Chronic idiopathic urticaria is a condition in which hives or rashes that appear on the skin have no known cause.

Outbreaks may happen without any triggers at all.

Learn more about urticaria.

In rare cases, a type 1 allergy can trigger chronic idiopathic urticaria. Type 2 allergies are exaggerated immune responses, which the body’s IgE antibodies control.

These allergies include atopic conditions, such as allergic:

They also include immune responses to allergens, such as:

  • anaphylaxis, which is a severe allergic reaction that can develop quickly and may be life threatening
  • urticaria
  • angioedema, which is swelling resulting from fluid buildup under the skin
  • food
  • medications

Several types of medication, such as antibiotics, aspirin, and ibuprofen, can trigger hives.

These medications can trigger the skin condition straight away, within days or weeks, or even years after a person starts taking them.

Stress causes the body to release adrenaline. This can result in hives that appear quickly and last for 30–60 minutes.

Learn more about the effects of stress on the body.

Pet allergies, including reactions to cats and dogs, can trigger hives. People can come into contact with pet hair at work, at school, in day care, and in other indoor environments, even when no animal is present.

Learn more about animal allergies.

Physical urticaria means hives that have a physical cause. For instance, rubbing or scratching the skin is the most common cause of physical urticaria.

The hives can appear within a few minutes but usually last less than an hour.

Several foods can trigger hives, such as nuts, peanuts, eggs, and shellfish. The hives usually develop within one hour of eating the trigger food.

Foods such as bananas, chestnuts, kiwis, and mangos can also trigger hives in people with a latex allergy.

Sometimes it is the additives in a food rather than the food itself that trigger a person’s hives — for instance, food colorings and preservatives, such as sorbic acid.

In these two scenarios, the hives normally develop within 12–24 hours of eating the food.

Additives in vitamin supplements and other supplements, spices, cosmetics, and personal care products can also trigger hives within 12–24 hours of use.

Additionally, plants such as stinging nettle, cinnamon, and latex commonly trigger hives, which appear within minutes and can sometimes accompany difficulty breathing. This can also happen in case of contact with a jellyfish.

Other triggers can include:

  • exercise
  • heat and hot showers
  • cold
  • UV light
  • vibration (rarely)
  • pressure on the skin, such as from tight clothing or a purse strap
  • water (rarely)

Hives usually develop from an itchy patch of skin that changes into swollen welts.

Idiopathic means that doctors do not know what causes the hives, which appear spontaneously.


Chronic hives usually present with the same symptoms as hives that do not last as long.

Chronic tends to mean that the hives occur twice a week or more often and do not go away for 6 weeks or more.

Symptoms include raised itchy bumps, which are the same color as the skin, and blanching, which means that the center of a hive turns white when pressed.

When doctors define chronic urticaria as idiopathic, it means that there is no known trigger. However, immune-system-related causes can include an autoimmune reaction or a reaction to a food or drug that does not fit the definition of an allergy.

Additionally, an acute or chronic infection may cause chronic idiopathic urticaria — for instance, due to:

The first step in treating chronic idiopathic urticaria is avoiding any known triggers.

Doctors may also prescribe medications, such as antihistamines, and leukotriene receptor antagonists, which people take for chronic asthma, along with short bursts of corticosteroids to dampen the inflammatory response.

If the condition does not improve, doctors may refer a person to a specialist, who may then prescribe omalizumab or cyclosporine. These medications regulate the overreactivity of a person’s immune system.

More than half of people with chronic urticaria get rid of their symptoms or experience improvement within 1 year.

Chronic idiopathic urticaria is hives with no known cause. They usually develop at least twice a week for a period of at least 6 weeks.

Several environmental triggers may bring on the raised, itchy bumps — for instance, allergies, medications, stress, pet hair, food, stinging nettles, and UV light.

While doctors have not identified a single cause of chronic idiopathic urticaria, it may relate to an overactive immune system or an infection.

Besides avoiding triggers, a person can try taking antihistamines to reduce their symptoms. If these persist, a person can talk with their doctor about stronger prescription medications.